Antioxidants regulate functional activity and reduce the risk of development of diseases. Deficiency of antioxidants leads to sharp decrease in resistance to adverse factors. The vegetable food is the main and most available source of antioxidants for the human. Yacon (Polymnia sonchifolia Poepp. & Endl. syn. Smallanthus sonchifolia), a new perspective plant (сv. Yudinka originated by All-Russian Research Institute of Vegetable Breeding and Seed Production), was successfully introduced in Ukraine. The content of the biologically active substances (BAS) in plants is known to be influenced by transfer from the places of natural growth in other climatic conditions, and by biotic factors, too. Despite it, only a few papers are devoted to studying of the content of phenols, oligofructans and other BAS in the yacon depending on cultivation and storage conditions, and the data on an influence of pathogens on the BAS in the yacon are absent. Therefore our aim was to determine the level of the main BAS (phenolic compounds and fructosans) in yacon of the Ukrainian introduction (in leaves and root tubers), and also to estimate the influence of biotic factors.